Mobile communication system, mme, incoming call control method of mobile communication system, and incoming call control method of mme

ABSTRACT

It is aimed to provide a mobility management device that can normally provide a UE with a notification of an incoming voice call made when ISR is activated and when a mobile communication device is moving from a location registration area under control of an MME to a location registration area under control of an SGSN. A mobility management device ( 10 ) makes an ISR feature operate in collaboration with an SGSN ( 20 ). It is assumed that a location registration area ( 60 ) managed by the mobility management device ( 10 ) exists within a location registration area ( 50 ) managed by the SGSN ( 20 ), and an incoming voice call is made to a mobile communication device ( 30 ) during when the mobile communication device ( 30 ) is moving out of the location registration area ( 60 ). The mobility management device ( 10 ) includes an incoming voice call control unit ( 11 ) that, in the above case, sends a response message indicating that the mobile communication device ( 30 ) is moving to a switching device ( 40 ) and, when an incoming voice call message is sent again from the switching device ( 40 ) to a switching device ( 40 ) after the lapse of a specified period of time, performs call attempt to the mobile communication device ( 30 ).

TECHNICAL FIELD

The present invention relates to a mobility management device, acommunication system, an incoming voice call control method and aprogram and, for example, relates to a mobility management device, acommunication system, an incoming voice call control method and aprogram using the ISR feature. An incoming voice call described in thisinvention includes a multimedia communication such as a video telephone.

BACKGROUND ART

In the 3GPP (Third Generation Partnership Project) that defines astandard for mobile network systems, EPC (Evolved Packet Core) isspecified as the next generation mobile network system. The EPC is anetwork system that accommodates an LTE (Long Term Evolution) accessnetwork in addition to radio access networks called the secondgeneration and the third generation.

The state where a mobile communication device that is located in an LTEwireless area is connected to the EPC is referred to as “ECM-CONNECTED”state. The mobile communication device may be referred to as a mobileterminal device. Further, the mobile communication device is defined asa UE (User Equipment) in the 3GPP. Furthermore, a device that managesthe location of the UE that is located in the LTE wireless area is MME(Mobility Management Entity), and a device that manages the location ofthe UE that is located in the second and third generation wireless area(which is referred to as “3G wireless area”) is SGSN (Serving GPRSSupport Node).

It is anticipated that, initially after introduction of the LTE wirelessarea, the LTE wireless area will be gradually broadened, overlaying the3G wireless area. In the case where the LTE wireless area and the 3Gwireless area overlap and the LTE wireless area is small, switchingbetween the LTE wireless area and the 3G wireless area is anticipated tooccur frequently in the UE that is located at the end of the LTEwireless area. The frequent switching between the LTE wireless area andthe 3G wireless area causes problems such as an increase in networkprocessing load due to location registration processing and batteryconsumption of the UE.

In Non Patent Literature 1, the LTE/3G location registration skipfeature (ISR (Idle mode Signaling Reduction) feature; hereinafterreferred to as the ISR feature) that does not carry out locationregistration even when a UE moves to a different area unless there is nochange in the location registration area that has been registered beforein the LTE wireless area and the 3G wireless area. Enabling the ISRreduces the number of times location registration is carried out, and itis thereby possible to solve the problems of an increase in networkprocessing load and UE battery consumption.

CITATION LIST Non Patent Literature

-   [NPL 1] “SAE basic control technology to achieve the ALL-IP    network”, NTT DOCOMO Technical Journal, Vol. 17, No. 3, October 2009

SUMMARY OF INVENTION Technical Problem

In the case where a UE in the ECM-CONNECTED state is located in thelocation registration area under control of the MME and when an incomingvoice call is made from MSC(Mobile Switching Center)/VLR(VisitorLocation Register) to the UE, the MSC/VLR notifies the MME that anincoming voice call to the UE has occurred. The MME notifies the MSC/VLRthat it has received the incoming voice call to the UE. Further, the MMEnotifies the UE that the incoming voice call has arrived. At this time,the MSC/VLR stops a timer for retransmission of an incoming callnotification and enters a mode to wait for a response from the UEbecause the incoming voice call notification has been accepted. Notethat, if the MME sends an incoming call notification to the UE duringthe processing (handover) that the UE moves from the locationregistration area under control of the MME to the location registrationarea under control of the SGSN, the incoming call notification does notreach the UE in some cases.

If the UE is moved to the location registration area under control ofthe MME or the SGSN where the ISR is not activated, locationregistration for an incoming voice call is newly performed by the UE forthe MSC/VLR in the location registration area under control of the MMEor the SGSN where the ISR is not activated to which the UE is moved.Therefore, the MSC/VLR can notify the incoming voice call again to theUE located in the location registration area under control of the MME orthe SGSN where the ISR is not activated to which the UE is moved. On theother hand, when the UE is moved to the location registration area undercontrol of the SGSN where the ISR is activated, location registration isnot performed by the UE. Therefore, when the MME sends an incoming callnotification to the UE during handover of the UE and therefore theincoming call notification does not reach the UE, the MSC/VLR cannotnotify the incoming voice call again to the UE located in the locationregistration area under control of the SGSN where the ISR is activated,which causes a failure in an incoming voice call to the UE.

An exemplary object of the invention is to normally provide a UE with anotification of an incoming voice call that is made when ISR isactivated in an MME and an SGSN and when a mobile communication deviceis moving from a location registration area under control of the MME toa location registration area under control of the SGSN.

Solution to Problem

A mobility management device according to a first exemplary aspect ofthe invention is a mobility management device that makes an ISR featureoperate in collaboration with an SGSN and includes an incoming voicecall control unit that sends a response message indicating that a mobilecommunication device is moving to a switching device in response to anincoming voice call message notified from the switching device and, whenthe incoming voice call message is sent again from the switching deviceafter a lapse of a specified period of time, performs call attempt tothe mobile communication device through the SGSN, in a case where asecond location registration area managed by the mobility managementdevice exists within a first location registration area managed by theSGSN, and an incoming voice call is made to the mobile communicationdevice during when the mobile communication device is moving out of thesecond location registration area in the first location registrationarea.

A communication system according to a second exemplary aspect of theinvention includes an SGSN that manages a first location registrationarea, a mobility management device that manages a second locationregistration area overlapping a part of the first location registrationarea, and a switching device that notifies an incoming voice call to amobile communication device through the mobility management device, and,in a case where an incoming voice call is made to the mobilecommunication device during when the mobile communication device ismoving out of the second location registration area in the firstlocation registration area, the mobility management device sends aresponse message indicating that the mobile communication device ismoving to the switching device in response to an incoming voice callmessage notified from the switching device and, when the incoming voicecall message is sent again from the switching device after a lapse of aspecified period of time, performs call attempt to the mobilecommunication device through the SGSN.

An incoming voice call control method according to a third exemplaryaspect of the invention is an incoming voice call control methodexecuted in a mobility management device that makes an ISR featureoperate in collaboration with an SGSN, and, in a case where a secondlocation registration area managed by the mobility management deviceexists within a first location registration area managed by the SGSN,and an incoming voice call is made to a mobile communication deviceduring when the mobile communication device is moving out of the secondlocation registration area in the first location registration area, themethod sends a response message indicating that the mobile communicationdevice is moving to a switching device in response to an incoming voicecall message notified from the switching device and, when the incomingvoice call message is sent again from the switching device after a lapseof a specified period of time, performs call attempt to the mobilecommunication device through the SGSN.

A program according to a fourth exemplary aspect of the invention is aprogram executed by a computer of a mobility management device thatmakes an ISR feature operate in collaboration with an SGSN, the programcausing the computer to execute a step of sending a response messageindicating that a mobile communication device is moving to a switchingdevice in response to an incoming voice call message notified from theswitching device, and a step of performing call attempt to the mobilecommunication device through the SGSN when the incoming voice callmessage is sent again from the switching device after a lapse of aspecified period of time, in a case where a second location registrationarea managed by the mobility management device exists within a firstlocation registration area managed by the SGSN, and an incoming voicecall is made to the mobile communication device during when the mobilecommunication device is moving out of the second location registrationarea in the first location registration area.

Advantageous Effects of Invention

According to the invention, it is possible to provide a mobilitymanagement device, a communication system, a voice incoming call controlmethod and a program that can normally provide a UE with a notificationof an incoming voice call that is made when ISR is activated in an MMEand an SGSN and when a mobile communication device is moving from alocation registration area under control of the MME to a locationregistration area under control of the SGSN in the ECM-CONNECTED state.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram of a communication system according toa first exemplary embodiment;

FIG. 2 is a configuration diagram of a communication system according toa second exemplary embodiment;

FIG. 3 is a diagram showing a flow of processing to connect a UE to anetwork according to the second exemplary embodiment;

FIG. 4 is a diagram showing a flow of incoming voice call processingaccording to the second exemplary embodiment;

FIG. 5 is a diagram showing a flow of incoming voice call processingaccording to a third exemplary embodiment;

FIG. 6 is a diagram showing a flow of incoming voice call processingaccording to a fourth exemplary embodiment;

FIG. 7 is a diagram showing a flow of incoming voice call processingaccording to a fifth exemplary embodiment; and

FIG. 8 is a diagram showing a flow of incoming voice call processingaccording to a fifth exemplary embodiment.

DESCRIPTION OF EMBODIMENTS First Exemplary Embodiment

Exemplary embodiments of the present invention are described hereinafterwith reference to the drawings. A configuration example of acommunication system according to a first exemplary embodiment of theinvention is described with reference to FIG. 1. The communicationsystem shown in FIG. 1 is composed of node devices specified in the3GPP. The communication system in FIG. 1 includes a mobility managementdevice 10, an SGSN 20, a mobile communication device 30, and a switchingdevice 40.

The mobility management device 10 and the SGSN 20 make the ISR featureoperate in collaboration with each other. Stated differently, themobility management device 10 and the SGSN 20 enable the ISR featureincorporated in each of them. The SGSN 20 manages a locationregistration area 50. The mobility management device 10 manages alocation registration area 60. The location registration area 50includes the location registration area 60. Accordingly, a part of thelocation registration area 50 and the location registration area 60 areoverlapping areas.

In FIG. 1, the mobile communication device 30 moves out of the locationregistration area 60 in the location registration area 50.

The switching device 40 notifies the mobile communication device 30through the mobility management device 10 about an incoming voice call.In the case where the mobile communication device 30 is located insidethe location registration area 60, the switching device 40 notifies themobile communication device 30 through the mobility management device 10about the incoming voice call. In the case where the mobilecommunication device 30 is located outside the location registrationarea 60 and inside the location registration area 50, the switchingdevice 40 notifies the mobile communication device 30 through themobility management device 10 and the SGSN 20 about the incoming voicecall and the SGSN 20.

A configuration example of the mobility management device 10 isdescribed hereinafter. The mobility management device 10 includes anincoming voice call control unit 11. The case where an incoming voicecall is made to the mobile communication device 30 during the time whenthe mobile communication device 30 is moving out of the locationregistration area 60 in the location registration area 50 is described.“During moving” is the state where processing for movement of the mobilecommunication device 30 has not yet completed in the mobility managementdevice 10 and the SGSN 20 and, for example, the state where handoverprocessing for the mobile communication device 30 has not yet completedtherein.

In the case where the incoming voice call control unit 11 detects thatthe mobile communication device 30 has moved out of the locationregistration area 60 when an incoming voice call message is notifiedfrom the switching device 40, the incoming voice call control unit 11sends a response message indicating that the mobile communication device30 is during its movement to the switching device 40. For example, theincoming voice call control unit 11 may detect that the mobilecommunication device 30 has moved out of the location registration area60 when it performs incoming call processing for the mobilecommunication device 30 and then receives a notification thattransmission of an incoming voice call notification message to themobile communication device 30 has failed from a base station that hasbeen managing the mobile communication device 30. When an incoming voicecall is not normally notified to the mobile communication device 30through the mobility management device 10, the switching device 40retransmits the incoming voice call message after the lapse of aspecified period of time.

At the time when the incoming voice call message is retransmitted fromthe switching device 40 after the lapse of a specified period of time,the mobile communication device 30 has completed handover to theposition outside the location registration area 60 and inside thelocation registration area 50, and therefore the incoming voice callcontrol unit 11 sends a message indicating a call of the mobilecommunication device 30 to the SGSN 20. In other words, the mobilitymanagement device 10 performs call attempt to the mobile communicationdevice 30 through the SGSN 20.

As described above, with use of the communication device shown in FIG.1, even in the case where an incoming voice call is made to the mobilecommunication device 30 when the ISR feature is activated in themobility management device 10 and the SGSN 20 and during the time whenthe mobile communication device 30 is moving out of the locationregistration area 60 in the location registration area 50, the switchingdevice 40 can successfully notify the mobile communication device 30about an incoming voice call.

In general, in the case where the ISR feature is activated in themobility management device 10 and the SGSN 20, location registrationprocessing of the mobile communication device 30 is not executed evenwhen the mobile communication device 30 has moved out of the locationregistration area 60 in the location registration area 50. For example,in the case where an incoming voice call to the mobile communicationdevice 30 is made before movement processing of the mobile communicationdevice 30 ends, that is, before handover processing ends, the mobilitymanagement device 10 performs call attempt to the mobile communicationdevice 30, assuming that the mobile communication device 30 is locatedwithin the location registration area 60. At this time, if the mobilitymanagement device 10 accepts the incoming voice call message notifiedfrom the switching device 40, the switching device 40 stops aretransmission timer for the incoming voice call message and thereforedoes not retransmit the incoming voice call message to the mobilitymanagement device 10. In such a case, because the ISR feature isactivated, the mobile communication device 30 does not perform locationregistration processing for the switching device 40. Accordingly, theswitching device 40 does not have a chance to send the incoming voicecall message again to the mobile communication device 30 that has movedout of the location registration area 60.

Therefore, in the case where the mobility management device 10 fails incalling the mobile communication device 30, the switching device 40cannot send the incoming voice call message to the mobile communicationdevice 30.

On the other hand, with use of the communication device shown in FIG. 1,in response to an incoming voice call message notified from theswitching device, the mobility management device 10 sends a responsemessage indicating that the mobile communication device 30 is during itsmovement, instead of sending a message indicating that the incomingvoice call message is received, to the switching device 40. It isthereby possible to prevent the switching device 40 from stopping theretransmission timer, and the mobility management device 10 receives theincoming voice call message again after expiration of the retransmissiontimer in the switching device 40.

By the time when the mobility management device 10 receives the incomingvoice call message again, handover processing of the mobilecommunication device 30 has completed because of the lapse of aspecified period of time, and therefore it is possible to perform callattempt to the mobile communication device 30 through the SGSN 20. Theretransmission timer for an incoming voice call message in the switchingdevice 40 may be set in consideration of the execution time of handoverprocessing of the mobile communication device 30. As described above,with use of the communication device shown in FIG. 1, it is possible toreliably notify the mobile communication device 30 about the incomingvoice call message.

Second Exemplary Embodiment

A configuration example of a communication system according to a secondexemplary embodiment of the invention is described with reference toFIG. 2. The communication system shown in FIG. 2 includes an MME 15, anSGSN 20, a UE 35, an MSC/VLR 45, an eNB (evolved Node B) 70 and a 2G/3Gradio control device 80. The MSC/VLR 45 is connected to an externalnetwork.

The MME 15 is equivalent of the mobility management device 10 in FIG. 1.The MSC/VLR 45 is equivalent of the switching device 40 in FIG. 1. TheUE 35 is equivalent of the mobile communication device 30 in FIG. 1. TheeNB 70 is a base station device that manages the LTE wireless area. The2G/3G radio control device 80 is a radio control device that manages the2G or 3G wireless area. The 2G/3G radio control device 80 may be an RNC(Radio Network Controller) specified in the 3GPP, for example.

The UE 35 is a communication device that is specified as a mobilecommunication device in the 3GPP. The UE 35 may be a cellular phone, asmartphone, a tablet terminal, a personal computer with a communicationfunction or the like, for example. Further, the UE 35 may be an M2M(Machine To Machine) device that performs communications in anautonomous manner. The M2M device may be a device that does not oftenmove such as an automatic vending machine or an electrical appliancehaving a communication function, or a watch worn by a user and the like,for example.

Hereinafter, a flow of processing to connect the UE 35 to a network isdescribed with reference to FIG. 3. First, the UE 35 sends a CombinedAttach Request message to the MME 15 in order to make a request forregistration of a line attachment location (S11). Receiving the CombinedAttach Request message, the MME 15 generates location registrationinformation of the UE 35. The location registration information containsinformation indicating that the UE 35 is located within the locationregistration area managed by the MME 15 or subscriber information of theUE 35, for example. The subscriber information of the UE 35 may beacquired from a subscriber information management device (not shown)that is placed in the mobile communication system. The subscriberinformation management device is specified as HSS (Home SubscriberServer) in the 3GPP, for example.

Next, the MME 15 establishes SGs association with the MSC/VLR 45 (S12).The SGs association is used to send and receive an incoming voice callmessage (CS (Call Switch) control signal) between the MME 15 and theMSC/VLR 45. After establishing the SGs association with the MSC/VLR 45,the MME 15 sends a Combined Attach Accept message to the UE 35 (S13).

Then, the UE 35 sends a Routing Area Update Request message to the SGSN20 (S14). Receiving the Routing Area Update Request message, the SGSN 20generates location registration information of the UE 35.

Then, the location registration information is synchronized between theSGSN 20 and the MME 15 to enable the ISR (S15). The SGSN 20 then sends aRouting Area Update Accept message to the UE 35 (S16). After executionof the processing in Steps S11 to S16, the UE 35 and the MME 15 becomeECM-CONNECTED state (S17). The ECM-CONNECTED state is a state where acommunication path for user data is established between the network andthe UE 35.

A flow of incoming voice call processing for the UE 35 is describedhereinafter with reference to FIG. 4. It is assumed that the processingof FIG. 3 has been already performed before executing the processing ofFIG. 4, and the UE 35 and the MME 15 are in the ECM-CONNECTED state.

First, the MSC/VLR 45 receives an incoming voice call message sent froma voice network (S21). Next, the MSC/VLR 45 sends a Paging Requestmessage to the MME 15 (S22). The MSC/VLR 45 sends the Paging Requestmessage through the SGs association established between the MSC/VLR 45and the MME 15. In other words, the MSC/VLR 45 sends the Paging Requestmessage by the SGs interface. After sending the Paging Request message,the MSC/VLR 45 starts a retransmission timer that specifies the timingto retransmit the Paging message (S23).

Even when the MME 15 receives the Paging Request message, it does notsend a response message (Service Request message) indicating that anincoming voice call is accepted to the MSC/VLR 45. If an incoming voicecall is accepted by the MME 15, the MSC/VLR 45 stops the timer that hasbeen started to retransmit the incoming voice call message (PagingRequest message). Thus, in order to prevent the retransmission timerfrom stopping, the MME 15 does not send the Service Request message tothe MSC/VLR 45.

Then, the MME 15 sends a CS Service Notification message to notify theUE 35 through the eNB 70 about an incoming voice call (S24). It is notedthat the UE 35 starts moving out of the location registration area 60before the CS Service Notification message is sent from the eNB 70(S25). In this case, the eNB 70 abandons transmission of the CS ServiceNotification message to the UE 35 (S26) based on that fact that the UE35 has already started moving out of the location registration area 60.Note that, although the case where transmission of the CS ServiceNotification message to the UE 35 (S26) is abandoned is described in thefollowing description, when the eNB 70 sends the CS Service Notificationmessage to the UE 35 and then a response message (NAS extended ServiceRequest message) is sent from the UE 35 to the MME 15 after that, theMME 15 sends a Service Request message to the MSC/VLR 45 upon receivingthe NAS extended Service Request message.

Then, the eNB 70 sends a NAS Non-Delivery Indication message indicatingthat transmission of the CS Service Notification message to the UE 35has failed to the MME 15 (S27). Receiving the NAS Non-DeliveryIndication message, the MME 15 sends a paging reject message to whichcause is set indicating failure of transmission of the CS ServiceNotification message to the UE 35 due to movement of the UE 35 to theMSC/VLR 45 (S28).

Then, the eNB 70 sends a Handover Required message to the MME 15 inorder to start handover processing of the UE 35 (S29). The MME 15performs handover processing with the SGSN 20 (S30). After registrationof the UE 35 is done in the handover processing, the SGSN 20 sends aForward Relocation Complete Notification message to the MME 15 (S31).Then, the MME 15 sends a Forward Relocation Complete Acknowledge messageto the SGSN 20 as a response message to the Forward Relocation CompleteNotification message (S32). After the handover processing of the UE 35is completed in the above manner, the UE 35 and the SGSN 20 becomePMM-CONNECTED state. The PMM-CONNECTED state is a state where acommunication path for user data is established between the network andthe UE 35.

Then, when the retransmission timer for the Paging Request messageexpires, the MSC/VLR 45 retransmits the Paging Request message to theMME 15 (S35). The MME 15 then sends a CS Paging Indication message withan indication to perform call attempt to the UE 35 to the SGSN 20 sincethe UE 35 has already moved to the area under control of the SGSN 20(S36). The SGSN 20 then performs call attempt to the UE 35 (S37).

As described above, by executing the incoming voice call processingshown in FIG. 4, it is possible to prevent the retransmission timer fromstopping in the MSC/VLR 45. The MSC/VLR 45 can thereby send the PagingRequest message again to the MME 15 and therefore notify the UE 35 afterthe handover is done about an incoming voice call.

Third Exemplary Embodiment

A flow of incoming voice call processing for the UE 35 according to athird exemplary embodiment of the invention is described hereinafterwith reference to FIG. 5. It is assumed that the processing of FIG. 3has been already performed before executing the processing of FIG. 5,and the UE 35 and the MME 15 are in the ECM-CONNECTED state.

First, the UE 35 starts moving out of the location registration area 60in the location registration area 50 (S41). Next, the eNB 70 sends aHandover Required message to the MME 15 in order to start handoverprocessing of the UE 35 (S42). In the EPC, which is the network, theHandover Required message is the first message in the handoverprocessing. The MSC/VLR 45 receives an incoming voice call message sentfrom the voice network (S43). The MSC/VLR 45 then sends a Paging Requestmessage to the MME 15 (S44). After sending the Paging Request message,the MSC/VLR 45 starts the retransmission timer that specifies the timingto retransmit the Paging message (S45).

FIG. 5 is different from FIG. 4 in that the MME 15 receives the PagingRequest message after receiving the Handover Required message. In thecase of receiving the messages in this order, the MME 15 does notperform processing that accompanies reception of the Paging Requestmessage. Specifically, in FIG. 5, the MME 15 does not perform theprocessing in Steps S24 to S28 in FIG. 4. In other words, the MME 15does not perform transmission of the CS Service Notification message tothe UE 35, which is processing in response to reception of the PagingRequest message, and abandons or discards the Paging Request message. Onthe other hand, the MME 15 preferentially performs processing thataccompanies reception of the Handover Required message, rather thanprocessing that accompanies reception of the Paging Request message,which is incoming call processing to the UE 35.

Steps S46 to S53 are the same as Steps S30 to S37 in FIG. 4 and notredundantly described in detail. In this figure, the MME 15 does notsend the CS Service Notification message to the eNB 70 when it firstreceives the Paging Request message sent from the MSC/VLR 45 in StepS44. When the Paging Request message is sent in Step S51 upon expirationof the retransmission timer in the MSC/VLR 45, the MME 15 performs callattempt to the UE 35 through the SGSN 20.

As described above, by performing the flow of the incoming voice callprocessing in FIG. 5, even when an incoming voice call is made to the UE35 during execution of handover processing of the UE 35, it is possibleto notify the UE 35 about the incoming voice call after completion ofthe handover processing of the UE 35.

Further, the MME 15 does not perform incoming voice call processing inresponse to the Paging Request message received first, and performs callattempt to the UE 35 only after the Paging Request message isretransmitted after that, which allows reduction of the number ofsignals in the network compared to the case of FIG. 4. It is therebypossible to simplify the flow of the incoming voice call processing andreduce the processing load of the network.

Third Exemplary Embodiment

A flow of incoming voice call processing according to a third exemplaryembodiment of the present invention is described hereinafter withreference to FIG. 6. It is assumed that the processing of FIG. 3 hasbeen already performed before executing the processing of FIG. 6, andthe UE 35 and the MME 15 are in the ECM-CONNECTED state. Steps S61 toS69 are the same as Steps S41 to S49 in FIG. 5 and not redundantlydescribed in detail.

In FIG. 6, at the time when the UE 35 and the SGSN 20 have become thePMM-CONNECTED state (S69) after completion of handover processing, theMME 15 sends a CS Paging Indication message to the SGSN 20 if it hasreceived the Paging Request message during the handover processing(S70). Note that the MME 15 determines that the UE 35 and the SGSN 20have become the PMM-CONNECTED state (S69) by sending a ForwardRelocation Complete Acknowledge message to the SGSN 20 in Step S68 andthen sends a CS Paging Indication message to the SGSN 20 (S70).

In FIG. 5, the MME 15 sends the CS Paging Indication message to the SGSN20 upon transmission of the Paging Request message from the MSC/VLR 45.On the other hand, in this figure, the MME 15 sends the CS PagingIndication message to the SGSN 20 upon completion of handover processingwithout waiting for retransmission of the Paging Request message, whichis different from the processing of FIG. 5.

To implement the processing of this figure, the incoming voice callcontrol unit 11 of the MME 15 needs to know that the Paging Requestmessage has been received from the MSC/VLR 45 in Step S64. For example,the incoming voice call control unit 11 may have a Paging Requestmessage reception flag or the like and set the flag to on when itreceives the Paging Request message.

As described above, by performing the flow of the incoming voice callprocessing in FIG. 6, even when an incoming voice call is made to the UE35 during execution of handover processing of the UE 35, it is possibleto notify the UE 35 about the incoming voice call after completion ofthe handover processing of the UE 35.

Further, the MME 15 can send the CS Paging Indication message to theSGSN 20 without waiting for retransmission of the Paging Requestmessage, and it is thereby possible to perform call attempt to the UE 35earlier than the case of FIG. 5.

Fourth Exemplary Embodiment

A flow of incoming voice call processing according to a fourth exemplaryembodiment of the present invention is described hereinafter withreference to FIG. 7. It is assumed that the processing of FIG. 3 hasbeen already performed before executing the processing of FIG. 7, andthe UE 35 and the MME 15 are in the ECM-CONNECTED state. Steps S81 toS87 are the same as Steps S41 to S47 in FIG. 5 and not redundantlydescribed in detail.

In Step S88, the MME 15 sends a Forward Relocation Complete Acknowledgemessage as a response signal to the Forward Relocation CompleteNotification message sent from the SGSN 20 (S88). In this step, the MME15 sets information indicating execution of calling to the UE 35 to theForward Relocation Complete Acknowledge message. Specifically, the MME15 sets information which is set to the CS Paging Indication message inStep S36 of FIG. 4 to the Forward Relocation Complete Acknowledgemessage and sends it.

Because the MME 15 sets information which is set to the CS PagingIndication message to the Forward Relocation Complete Acknowledgemessage and sends it in Step S88, it is possible to notify the UE 35about completion of handover processing and further indicate calling.

Next, upon completion of the handover processing, the UE 35 and the SGSN20 become the ECM-CONNECTED state (S89). Then, the SGSN 20 performs callattempt to the UE 35 based on the indication of calling to the UE 35notified in Step S88 (S90).

As described above, by performing the flow of the incoming voice callprocessing in FIG. 7, even when an incoming voice call is made to the UE35 during execution of handover processing of the UE 35, it is possibleto notify the UE 35 about the incoming voice call after completion ofthe handover processing of the UE 35.

Further, the MME 15 sets information indicating execution of calling tothe UE 35 to the Forward Relocation Complete Acknowledge message thatnotifies completion of handover processing. This eliminates the need tosend the CS Paging Indication message which is sent in Step S70 of FIG.6 and thereby reduces the number of messages between the MME 15 and theSGSN 20. It is thereby possible to reduce the processing load of thenetwork.

Furthermore, because the number of messages can be reduced compared withthe case of FIG. 6, it is possible to perform call attempt to the UE 35earlier than the processing of FIG. 6.

A flow of incoming voice call processing for the UE 35 is describedhereinafter with reference to FIG. 8. FIG. 8 shows the operation in thecase where a conflict between handover processing and incoming voicecall processing does not occur and a notification of an incoming voicecall is successfully given to the UE 35, for comparison with theoperation examples shown in FIGS. 4 to 7. It is assumed that theprocessing of FIG. 3 has been already performed before executing theprocessing of FIG. 8, and the UE 35 and the MME 15 are in theECM-CONNECTED state.

First, the MSC/VLR 45 receives an incoming voice call message sent froma voice network (S91). Next, the MSC/VLR 45 sends a Paging Requestmessage to the MME 15 (S92). After sending the Paging Request message,the MSC/VLR 45 starts the retransmission timer that specifies the timingto retransmit the Paging message (S93).

Then, the MME 15 sends a CS Service Notification message to notify theUE 35 through the eNB 70 about an incoming voice call (S94).

Receiving the CS Service Notification, the UE 35 sends a NAS extendedService Request message to the MME 15 through the eNB 70 (S95).

Receiving the NAS extended Service Request message, the MME 15 sends aresponse message (Service Request message) indicating that an incomingvoice call is accepted to the MSC/VLR 45 (S96). The response message(Service Request message) can also notify the MSC/VLR 45 that the UE 35is in the ECM-CONNECTED state. When the incoming voice call is acceptedby the MME 15, the MSC/VLR 45 stops the timer that has been started toretransmit the incoming voice call message (Paging Request message). Bythis operation, processing to retransmit the Paging Request message inthe MSC/VLR 45 is stopped (S97). After that, the UE 35 moves to the 3Gwireless area, and an incoming call operation using the 2G/3G radiocontrol device 80 and the MSC/VLR 45 is continued (S98).

Although the present invention is described as a hardware configurationin the above exemplary embodiments, the present invention is not limitedthereto. The present invention may be implemented by causing a CPU(Central Processing Unit) to execute a computer program to performprocessing of the mobility management device, the switching device orthe SGSN.

In the above example, the program can be stored and provided to thecomputer using any type of non-transitory computer readable medium. Thenon-transitory computer readable medium includes any type of tangiblestorage medium. Examples of the non-transitory computer readable mediuminclude magnetic storage media (such as floppy disks, magnetic tapes,hard disk drives, etc.), optical magnetic storage media (e.g.magneto-optical disks), CD-ROM (Read Only Memory), CD-R, CD-R/W, andsemiconductor memories (such as mask ROM, PROM (Programmable ROM), EPROM(Erasable PROM), flash ROM, RAM (Random Access Memory), etc.). Theprogram may be provided to a computer using any type of transitorycomputer readable medium. Examples of the transitory computer readablemedium include electric signals, optical signals, and electromagneticwaves. The transitory computer readable medium can provide the programto a computer via a wired communication line such as an electric wire oroptical fiber or a wireless communication line.

It should be noted that the present invention is not limited to theabove-described exemplary embodiments but is susceptible of numerouschanges and modifications as known to those skilled in the art; forexample, the 2G/3G radio control device 80 may be a 3G radio controldevice, and the MSC/VLR 45 may be composed of separate MSC and VLRdevices.

While the invention has been particularly shown and described withreference to exemplary embodiments thereof, the invention is not limitedto these embodiments. It will be understood by those of ordinary skillin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the claims.

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2013-079961 filed on Apr. 5, 2013 andJapanese patent application No. 2013-141828 filed on Jul. 5, 2013, thedisclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

-   10 MOBILITY MANAGEMENT DEVICE-   11 INCOMING VOICE CALL CONTROL UNIT-   15 MME-   20 SGSN-   30 MOBILE COMMUNICATION DEVICE-   35 UE-   40 SWITCHING DEVICE-   45 MSC/VLR-   50 LOCATION REGISTRATION AREA-   60 LOCATION REGISTRATION AREA-   70 eNB-   80 2G/3G RADIO CONTROL DEVICE

1-13. (canceled)
 14. A terminal (UE (User Equipment)) used in a mobilecommunication system, comprising: a unit that supports access to a basestation (eNB) and a 2G/3G radio control device; a unit that performshandover procedure from an LTE (Long Term Evolution) wireless area to a3G wireless area or a 2G wireless area; and a unit that receives, if thehandover procedure is ongoing when an MME receives a paging requestmessage over an SGs interface between the MME and an MSC/VLR (MobileSwitching Center/Visitor Location Register), and hence the MME discardsthe paging request message and performs no further action, the pagingrequest message retransmitted by the MSC/VLR from the base station. 15.The terminal according to claim 14, wherein the MME does not performfurther incoming call processing to the terminal after discarding thepaging request massage and, when receiving retransmission of the pagingrequest message from the MSC/VLR, continues the incoming callprocessing.
 16. The terminal according to claim 15, wherein the MSC/VLRperforms retransmission of the paging request message by starting atimer.
 17. A communication method performed by a terminal (UE (UserEquipment)) used in a mobile communication system, comprising:supporting access to a base station (eNB) and a 2G/3G radio controldevice; performing handover procedure from an LTE (Long Term Evolution)wireless are to a 3G wireless area or a 2G wireless area; and receiving,if the handover procedure is ongoing when an MME receives a pagingrequest message over an SGs interface between the MME and an MSC/VLR(Mobile Switching Center/Visitor Location Register), and hence the MMEdiscards the paging request message and performs no further action, thepaging request message retransmitted by the MSC/VLR from the basestation.
 18. The communication method by a terminal according to claim17, wherein the MME does not perform further incoming call processing tothe terminal after discarding the paging request massage and, whenreceiving retransmission of the paging request message from the MSC/VLR,continues the incoming call processing.
 19. The communication method bya terminal according to claim 18, wherein the MSC/VLR performsretransmission of the paging request message by starting a timer.